viral protein cages as building blocks for functional materials
Natural proteins, are essential ingredients in living life, which involve almost all fundamental processes including catalysis, metabolism, transcription and translation, transport and structural integrity. Nature builds up proteins by a bottom-up approach from the amino acids to large protein chains with tertiary three dimensional structures, and use proteins as highly efficient molecular machines that control many of the functions of living cell. Proteins that assemble in a well-defined way have attracted great interests in as building blocks in nanotechnology and materials science. Among these protein assemblies, virus particles have shown great advantages as they exist in various sizes and shapes, but with high monodispersity and symmetry. In addition, they can be easily produced in various methods at a large scale for laboratory research and the resultant products can potentially be scaled up for daily life applications. Based on the natural properties of virus coat proteins, they have been widely used for controlled drug loading and delivery, as size selective catalyst platforms, and confined nanoreactors for controlled growth of inorganic or organic materials. The research presented in this thesis describes strategies to take full advantages of virus protein capsids to develop functional materials.
This thesis provides insight into the impact of viral particles as scaffolds for functional materials; these are factors such as the surface electrostatic potential and pore size of the virus capsids, the chemical modification of the capsid surfaces and the high degree of monodispersity of these protein nanoparticles. In a model catalytic reaction, i.e. the reduction of nitro aromatics under the influence of gold nanoparticles encased in the capsid, the effect of the electrostatic potential and the pore size of virus-based protein cages on the accessibility of substrates with different charge and shape was studied first (Chapter 3). By taking advantage of the functional groups on the exterior surface of capsids, the gold/protein hybrid nanoparticles were immobilized in flow channels, a reactor that can be easily handled and be used under continuous flow can be obtained, the functionality of the individual hybrid nanoparticles is maintained (Chapter 4). Alternatively, cross-linking of the gold loaded protein on a liquid-liquid interface cages resulted in free standing thin films. The catalytic properties of these thin films were studied for potential application in bio-sensors. Also the biocompatibility of these thin films was studied, to reveal the possibility of in vivo applications, such as dynamic photo-thermotherapy by gold loaded thin films (Chapter 5).
In addition to construction hybrid nanoparticles based on the virus capsid and gold, the protein cages were also used as templates for controlled synthesis of inorganic, silica particles, where the growth was fine-tuned by controlling the pH When using gold loaded protein cages as template for silication, gold core-silica hollow shell nanostructures were formed after removing of organic components by high temperature calcination (Chapter 6). Finally, viruses and their hybrid nanoparticles were assembled into high ordered two-dimensional (2D) thin films on a surface. These results demonstrate that the virus particles can be used as environmental friendly porogens for the fabrication anti-reflective coatings (Chapter 7).
Overall, we have developed virus-based protein cage functional materials for catalysis and optical coatings. The unique properties of the viral particles, such as in vitro reversible self-assembly with functional nanoparticles or molecules incorporated, their capability of chemical or genetic modification and the ability to self-assembly into high-order structures, were employed to introduce new or different functions into these catalytic and/or optical materials. These studies help to gain further insight in the development of virus-based materials.
